To be exact, Hunminjeongeum (훈민정음) is what the King Sejong actually created. It is, in addition to the stated goal, thought to be the ultimate linguistic geekery by the King because one of the first books printed in Hunminjeongeum was Dongguk Jeongun [1], which set out to standardize the "orthodox" Chinese pronunciation in Korea. As always that didn't go well; the book does tell a lot about the Middle Korean despite of its failure.
[1] https://en.wikipedia.org/wiki/Dongguk_Jeongun